Mineralized ore such as uranium deposits is currently mainly accessed from subsurface locations using two different techniques that have been utilized for centuries. First, open pit mining uses large earth-moving equipment and blasting techniques to uncover the mineralized ore for removal. Second, underground mining uses underground ramps or shafts to access a level that can utilize standard underground mining machinery to remove the ore and lift or haul it to surface. There are obstacles for such conventional methods when accessing and mining certain ore bodies that are non-conducive to open pit or underground methods.
Open pit mining costs exponentially increase as the mineralized ore target increases in depth, resulting in this method primarily focusing on shallower ore bodies. When open pit mining for uranium in pressurized water saturated ground, dewatering is necessary; certain jurisdictions require treatment of the water prior to release into the environment, which can add significant cost to the mine life. Open pit mining produces a large environmental footprint for the pit and waste rock piles which have to be planned to be decommissioned in an environmentally sustainable way. When mining uranium, workers in the pit are also exposed to higher levels of gamma radiation, radioactive dust and radon gas primarily because of the proximity of the uranium ore to the workers.
Underground mining requires large initial capital outlays prior to production which reduces the economic incentive of this method by pushing out future positive cash flows into the future. An economic problem also exists when resources are too deep to be accessed with conventional open pit processes and the resource estimation is too small to justify underground mine upfront capital costs.
Technical problems also exist in underground mining of water bearing formations that are geo-technically weak and highly permeable. Considerable hydrostatic pressure from the surrounding formation could cause a sudden large water inflow when performing underground works, and in an underground mine setup this may cause at minimum production delays and at maximum risk to worker safety and loss of the mine. Mining uranium ore with a human-entry underground mining method may also pose increased risk to worker safety from a radiation protection point of view depending on uranium grades, geometry of the access, ventilation and exposure time.
What is needed, therefore, is a method that provides an economically sound mining alternative for subsurface deposits and can be applied in a manner that addresses safety issues such as radioactivity of the target ore.